A polyimide film has excellent thermal and mechanical properties. Therefore, as the demand for materials for high temperature has increased, the use of polyimide films has been lately required. However, the use of polyimide films has been restricted because they are expensive.
In particular, recently, polyimide films having excellent thermal and mechanical properties as well as optical properties have attracted considerable attention in the field of displays.
Thus, as the demand for polyimide films which have excellent thermal, mechanical and optical properties and which are cheaper has increased, attempts to mix polyamide with polyimide which is the main material of a polyimide film or to copolymerize a polyamide with a polyimide have been made.
However, currently, polyamide-imide copolymer films satisfying optical properties as well as thermal and mechanical properties are not on the market yet.